The first commercial scale carbon-capture project captures CO2 from a 55-year-old coal-fired plant near Estevan, Saskatchewan, and stores it in nearby underground sites.

Credit: SaskPower

CARBON CAPTURED HERE

The first commercial scale carbon-capture project captures CO2 from a 55-year-old coal-fired plant near Estevan, Saskatchewan, and stores it in nearby underground sites.

Credit: SaskPower

At Saskatchewan’s Boundary Dam power plant, not far from the U.S. border with North Dakota, one of its generating units burns some 800,000 tons of coal each year to provide about 139 MW of electricity to businesses and homes in the region. But since late 2014, the carbon dioxide produced by that burning has had a new fate: Instead of flitting up the smoke stack and out into the atmosphere, it gets trapped and compressed. The utility, SaskPower, then sends most of the CO2 along a pipeline to a nearby oil field where it is pumped underground to push oil out from below. About 2 km west of the plant, SaskPower injects the remaining portion 3.4 km deep into the Deadwood Formation, a brine-saturated sandstone formation, for permanent storage.

Janet Pelley is a freelance writer. A version of this story first appeared in ACS Central Science: http://cenm.ag/ccapture.

This snatching of CO2 before it escapes the plant and stuffing it away, known as carbon capture and storage (CCS), could decouple the burning of fossil fuels from its resulting climate-changing emissions. While some have criticized CCS as an environmentally and financially risky technology that props up the coal industry at the expense of research into renewables, most experts say it is a necessary tool for limiting climate change, and—like it or not—it will be widely deployed in the future. “The rate at which wind and solar power are growing is being outpaced by population growth and the rate at which energy demand is increasing,” says Christopher W. Jones, a chemical engineer at Georgia Tech. For the next 50 years, he says, fossil energy will supply the majority of society’s power needs. “If we really care about climate change, there is no choice but to implement CCS.”

The problem is that CCS is currently too expensive to be practical, so researchers are seeking new technologies to make it cheaper. Scientists are also working on ways to ensure the CO2 stays put after it is buried. Combined with the political will to reduce carbon emissions, these advancements could see much more carbon captured and stored in coming years.

Paris Climate Talks

A pivotal moment for climate change is here as nations are meeting in Paris for climate talks this week. In September this year, the world’s two largest greenhouse gas emitters, the U.S. and China, strengthened an earlier pledge to curb their carbon emissions, joining more than 150 other countries that have committed to do the same. This has raised hopes that the Paris meetings will produce a binding pact to cut greenhouse gas emissions, something previous climate talks have failed to achieve.

To cut future CO2 emissions enough to prevent catastrophic climate change, leading bodies such as the UN’s Intergovernmental Panel on Climate Change (IPCC) say CCS will be necessary; we cannot move away from coal fast enough to avoid emissions any other way. In its latest assessment report in 2014, the IPCC said that, without CCS, nations will have less than a 50% chance of staying below a global average temperature increase of 2 °C, a limit established by previous climate talks. To achieve this at the lowest cost, modeling by the International Energy Agency calls for 13% of needed emissions cuts to come from CCS.

Boundary Dam’s 139-MW unit now captures 1 million metric tons of CO2 per year, roughly 90% of its emissions, but it cost $1.3 billion. Despite the cost, the project went ahead because Canadian regulations require old burners to either convert to CCS or shut down. In addition, the company obtained a $240 million subsidy from the Canadian government and found a buyer for most of the CO2, notes Howard J. Herzog, a chemical engineer at Massachusetts Institute of Technology. “To justify the cost of CCS, you either need policy to force CO2 emissions reduction or government support or both,” he adds.

A fundamental barrier is the thermodynamics of the CO2 capture process, Herzog says. Today’s benchmark CCS technology, amine scrubbing, used in the Boundary Dam plant, consumes roughly 20–30% of the energy produced by a coal plant to capture and sequester its CO2 emissions, dramatically reducing a plant’s overall efficiency. During the process, CO2 bubbles up through a column filled with an alkaline amine solution, pulling the acidic CO2 molecules out of the air and into the solution. The CO2-laden liquid then flows to a heater, where the CO2 molecules evaporate from the mix and are trapped and compressed. Most of the energy used goes to heat the aqueous amine solution to 100–150 °C after scrubbing to regenerate the solution and capture the CO2. Water’s high heat capacity means this step takes a lot of energy.

A Solid Approach

A manganese-based metal–organic framework (MOF) binds CO2 in its pores in a chain reaction that leads to rapid saturation of the MOF. Mn (green), C (gray), O (red), N (blue), and H (white) atoms are shown.

Credit: Jeffrey R. Long

CARBON GRABBER

A manganese-based metal–organic framework (MOF) binds CO2 in its pores in a chain reaction that leads to rapid saturation of the MOF. Mn (green), C (gray), O (red), N (blue), and H (white) atoms are shown.

Credit: Jeffrey R. Long

To cut capture costs, scientists are turning to solid adsorbents, which have a substantially lower heat capacity than water. One such adsorbent was developed by Jones at Georgia Tech. He and his team incorporated solid particles made of polyethylenimine-silicon dioxide (PEI) into hollow plastic fibers about 1 mm in diameter, which they bundled into a tube before passing flue gases through it. The PEI particles adsorb CO2 through the same chemistry as liquid amines. Then to recover it, the scientists heat the fibers by running hot water down the center, releasing a stream of concentrated CO2 on the outside of the fibers. The high surface area provided by the fibers allows a lot of contact between gas and sorbent, Jones says. Also, the capture and release steps take place in the same vessel, making the process simpler and potentially cheaper than amine scrubbing, which requires a separate unit for each.

Meanwhile, the CCS community is abuzz over the potential of metal–organic frameworks (MOFs), porous structures built of metal ions linked by organic molecules. They have an enormous internal surface area, and those made of the right material can adsorb a lot of CO2, says Jeffrey R. Long, a chemist at the University of California, Berkeley. He and his colleagues designed magnesium- or manganese-based MOFs with diamine molecules loaded into the pores. When CO2 enters the cylindrical pores of the MOF, it binds to a diamine in a way that makes it easier and faster for the next CO2 molecule to bind the neighboring diamine molecule, promoting a chain reaction that quickly saturates the MOF. When the scientists raise the temperature by only 50 °C, the CO2 comes flooding off the framework.

MOFs are expensive, however, says Jennifer Wilcox, a chemical engineer at Stanford University. She and her colleagues have engineered a cheaper, carbon-based sorbent, similar to activated carbon, with embedded nitrogen functional groups and controllable pore structure that can be optimized to select for CO2. The material can be quickly cooled and heated. Also, CO2 nestles into the pores without forming a chemical bond, so it takes little energy to desorb the CO2.

Even better than sorbents could be membranes that separate CO2 from the flue gas, Wilcox adds, because then there’s no sorbent to regenerate and no water to heat. Gas separation membranes typically rely on a concentration or pressure difference across the membrane to drive the desired molecules through, but coal plant flue gas is only 14% CO2 by volume, too low to provide a driving force. Instead Wilcox and her colleagues created a membrane that is selective for the most abundant gas in power plant exhaust: nitrogen. The vanadium-based membrane allows nitrogen to pass, leaving CO2, water, and other trace gases behind on the other side.

All of these approaches are still at the research stage, but if any of them became practical, they could dramatically reduce the energy and cost penalties of CCS.

Still, researchers agree that what’s really needed to make CCS viable, regardless of the approach, is a price on carbon. Otherwise, why should a plant incur any cost if emitting CO2 to the atmosphere is free?

A Storage Problem

In this geologic cross section, supercritical CO2 is stored underground in porous rock beneath a layer of impermeable shale.

Credit: Global CCS Institute

DEEP STORAGE

In this geologic cross section, supercritical CO2 is stored underground in porous rock beneath a layer of impermeable shale.

Credit: Global CCS Institute

Carbon dioxide does, in some cases, have a value, and a hot area of research includes looking for ways to turn captured CO2 into valuable products that would offset the cost of capturing it. These run the gamut from carbonating beverages, making it into materials like plastics or concrete, feeding it to plants in enclosed greenhouses, or converting it back into methane or liquid fuel. But so far these are all niche applications or ideas at the research phase. “If you used CO2 for every product you can imagine, it would only consume about 20% of all the CO2 we produce,” says Ryan P. Lively, a chemical engineer at Georgia Tech. If any substantial fraction of the carbon emitted from coal plants is captured, for now, most of it will have to be buried.

Critics have raised perhaps the greatest concern about this step: If storage facilities leaked CO2 back into the atmosphere, it would undo the climate benefit from capturing it and tucking it away. But decades of oil and gas industry experience in enhanced oil recovery demonstrate that the storage technology works, says Grant Bromhal, an engineer at the Department of Energy’s National Energy Technology Laboratory.

For massive deployment of CCS, deep saline aquifers would likely be the major storage site. These reservoirs typically lie some 2–4 km below the surface of the Earth, composed of 50-m-thick, porous sandstone filled with saline water. The U.S. has enough of these formations to store 2,600 billion metric tons of CO2, sufficient for centuries of emissions. The CO2 stays put in such formations because they lie beneath impermeable shale, and capillary pressure in the sandstone pores locks the CO2 in place. Over time, the brine reacts with the CO2 to form solid calcium carbonate.

A Statoil natural gas plant in Norway has been storing 1 million metric tons per year in saline rock under the North Sea for 20 years with no evidence of leakage, but no one has tested projects as large as what a coal plant would produce—perhaps three to four times as much as the Statoil project. Uncertainties remain about how CO2 injected underground will travel and behave over time. DOE’s National Risk Assessment Partnership aims to study such concerns and develop best practices for CO2 injection, Bromhal says. For example, while fresh CO2-saturated brine readily dissolves cement in the lab, wells in the field have not degraded over four decades of use. The reason appears to be that the cement does not dissolve when the flux of brine over cement is intermittent. In fact, under these conditions, the cement changes the chemistry of the brine, leading to mineral precipitation and self-sealing of cracks. “We are now looking at ways to enhance the precipitation reaction in cements,” he says, which could help make storage safer.

Transitional Technology

Even if CO2 can be efficiently captured and safely stored, that does not mean countries should continue to rely on coal, which has other health and environmental impacts beyond climate change. But CCS can help society transition to a low carbon future, says Steve Clemmer of the Union of Concerned Scientists. And CCS is not just for coal plants, says Georgia Tech’s Lively. Industries such as cement and steel manufacturing produce large amounts of CO2 as part of the process chemistry. For these industries, the only way to avoid CO2 emissions is CCS.

North America now has 13 CCS projects either planned or in operation, launched as profit-making enhanced oil-recovery operations or as demonstrations with government funding. China, the world’s largest coal producer, is second in the world for CCS, with plans for nine large-scale projects. China is interested in CCS because it has numerous coal gasifiers that produce a large volume of CO2 that could be used to push oil out of the ground or as an industrial feedstock, says John Thompson, director of the fossil transition program at the Clean Air Task Force, an advocacy group. In 2011, the Shidongkou coal plant in Shanghai began capturing 100,000 tons of CO2 per year, which it sells to the beverage industry.

With the right outcome in Paris, experts agree that CCS could take off very fast. Technological improvements combined with commitments to make big cuts to carbon emissions—or a price on carbon to make cuts profitable—could allow the number of facilities to grow quickly. “The future of CCS will depend on political will to ensure deep, more than 50%, cuts in CO2 emissions,” says Simon J. Bennett, an energy analyst with the IEA. The Paris meetings will not emphasize any particular technology or specific strategies, but an agreement that is ambitious and acknowledges the role of innovation will support countries and companies developing CCS, he concludes. Then CO2 molecules around the world may share the fate of those at the Boundary Dam plant.

One of the best approaches for reducing atmospheric CO2 levels is chemical fixing. Therefore polycarbonate industry should be promoted as much as possible. An other important entry is described in this communication. If CO2 fixing can be made cheaper by the new method described here it would be an important step ahead. See to CO2 fixing: Is carbon dioxide a realistic raw material for chemical industry? L. Tacconi, K. Micskei, L. Caglioti, G. Palyi, Magyar Kem. Lapja, 63 (2008) 253-258.

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Steven Cooke (December 9, 2015 6:20 PM)

MAYBE if the world seriously addressed the ROOT CAUSE - increasing population and increased demand for higher living standards - we wouldn't waste so much energy on temporary 'fixes'. IF we can safely 'sequester' CO2, why not nuclear waste? And of course, the original question: WHAT is really the ideal "Global Temperature", and how was that derived (never mind regulating it there)?

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David Gedymin (December 12, 2015 3:42 PM)

I don't know that it's so much about an ideal global temperature per say, although certainly there is a range of tolerability for humanity (you wouldn't want it to be at -50F everywhere nor 150F). It's more about limiting the rate of change in temperature; the rate since the industrial revolution seems to be leading to more violent changes in climate and ecosystems. The climate always gradually changes, but I think the current rate is difficult for humanity to properly adapt.

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Chris Peterson (December 9, 2015 9:25 PM)

Has anyone looked into producing solids from CO2 in the air? Sea creatures routinely make calcium carbonate for shells and other body parts. How about genetically engineering a microorganism that can produce that as a waste product (in a safely contained environment)? Maybe there are other chemical reactions that can quickly and cheaply produce solids from atmospheric carbon. Long-term storage would be no problem for solids. Research on this approach should be encouraged.

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David Gedymin (December 12, 2015 3:48 PM)

I think the issue is that concentrations of CO2 in the air is only about 400 ppm. But think about it - producing cellulose from atmospheric CO2 is exactly what biological plants already do. That's where all the fossil fuels came from in the first place. But they rely entirely on using solar energy to do so, and that is limited. Wood represents recently stored solar energy, and that is not dense, while oil represents thousands upon thousands of stored solar energy - it's hard to beat that. I suppose another scenario would be using the flue gas / syngas in greenhouses to grow some sort of dense plant, dry out that biomatter using the heat integration, and either burn it or bury it.

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Jay G. Otten (December 10, 2015 12:49 AM)

Visualize the problem with capturing CO2 from coal or any fossil fuel. We have all seen trains loaded with coal moving down the railroad tracks. Now assume that for every carbon burned you come increase the molecular weight a little over three times. Now assume the CO2 is dry ice. Also the carbon content of coal is 60-80%; thus for every coal train you see you need to capture about 2.5 coal trains of CO2 if it were dry ice. That is a daunting prospect, especially when one considers the molecular weight of the compounds used to trap the CO2 relative to the CO2 itself. I hope the researchers succeed, but I believe it is Quixotic at best.

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David Gedymin (December 12, 2015 3:25 PM)

The article states that the U.S. has enough pourous sandstone structures to store 2,600 billion metric tons of CO2. It may be large in scale, but they apparently have the experience nad done the calculations to know that it is achievable.

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Peter Stilbs (December 10, 2015 3:48 AM)

CCS is a totally absurd idea - even to match present day emissions requires "plants" magnitudes larger than any chemical industry today, and enormous quantities of energy. Instead, let plants, algae and trees handle all this for free. They NEED this CO2 - and animal life on Earth totally depends on them too.

in today's politically correct World any mention of positive effects of CO2 emissions to the atmosphere is normally automatically met by hostile reactions of various kinds -

Regardless of that aspect and whether CO2 actually is a major climate driver it should be rather obvious to any thinking and educated person that carbon sequestration underground or capture by chemical means is a totally futile and mis-guided idea in any case. Just matching present-day emissions would require chemical plats 1000 times larger than any existing chemical or other industry, using up all available energy and other resources, and surely cause a grade of pollution unseen before.

The matter was discussed some years ago e.g. here https://www.newscientist.com/article/mg21428593-800-stripping-co2-from-air-requires-largest-industry-ever/

Norwegians abandoned their Mongstad sequestration project some years ago after pouring several billions into it - although it doubled as a means of pressing more oil out of the wells, where storage was meant to be made

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David Gedymin (December 12, 2015 3:39 PM)

Saying it is totally absurd is rather hyperbolic. 'Magnitudes' meaning what scale? Adding an Acid Gas Recovery unit and CO2 compressors might increase the plot space by 20-40%, but that certainly isn't 'magnitudes'.

There may be some local benefits to increased emissions. The hostility from people might come from somebody pointing out some benefits as though it outweighs the much more concerning impacts on climate change. Remember, this is about mitigating rapid human-caused climate that seems to be upsetting global weather patterns and ecosystems. This isn't about saving the planet itself - the planet will be fine. It's about keeping it habitable in the near-future so that humanity can adapt to climate that changes at a normal pace.

Again, where are you coming up with the idea that this would require plants 1000x times larger? That newscientist.com article you've cited is talking about scrubbing CO2 from dry atmospheric air, where the concentration of CO2 is only around 400 ppm. This is a drastically different scenario from scrubbing flue gas or syngas, where the concentration is closer to 23 mol%. Of course trying to efficiently remove CO2 at a concentration of 0.04% is absurd.

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Frank B. (December 11, 2015 12:55 AM)

There's absolutely no reason for this to be used to prop up "conventional" energy, aka dirty fossil fuels. Who says we need to do things the old way for another 50 years? Probably people who have no interest in fixing problems to begin with.

Let's see what boondoggles we can do to keep fossil fuels #1: Ethanol. Clean coal. Coal gasification. Algae biofuel. Now CCS. Anything to keep from doing the hard work of finding better ways to supply ourselves with energy - as if we don't have the wherewithal currently. It just needs to be improved and expanded, the way the current infrastructure has been built up over time to utilize fossil fuels.

CCS is stupid. We're already fracking, aren't we? And with all of the hazards associated with fracking -including polluted groundwater, wastewater that nobody knows what's in it, huge uses of freshwater, and of course, the fuel itself which is used and contributing to global warming- we also have to look at earthquakes, which have increased dramatically with the advent of increased fracking. So, combine earthquakes or any kind of ground/surface disruption with CCS, a breech of sorts, and what do you have? A point source of more CO2 gases instantly coming up into the air, negating the whole purpose of storage. You already have gas seepage (methane) into waters where fracking is done, CO2 is a little bigger molecularly, but I'm pretty sure it won't have a hard time doing the same things.

No, this is a bad, temporary solution to a long-term problem. You don't keep a paddleboat from sinking by sticking your foot through the hole. You plug the hole and then get the water out of it the best way you can. What we need to do with global warming is a comprehensive solution that involves mandatory energy efficiency (if not conservation); mandatory development, mandatory production, and mandatory mass utilization of abiotic renewables in power and transportation systems and modes; and CO2 abatement by air capture and chemical decomposition or synthesis into new products.

We already have CO2 sinks in the boreal forests of the North, which were buried long ago under now melting permafrost. This approach is wrong for many reasons. We've reduced forests significantly, and oceans aren't completely acting like the natural sinks they've always been, so we have to pull it out of the air where possible and stop continuing to put so much extra up there in the first place, until this can be corrected.

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Dr. Joop Koster (December 14, 2015 10:40 AM)

One could use the heat of the stack gases from coal-powered power plants to heat the CO2-alkanolamine loaded liquid in order to “ liberate “ CO2 from the alkanolamine .CO2 binds also better with ambient temperature alkanolamines.In a CCS unit, based on alkanolamine absorption chemistry , there are several ways to recuperate heat from hot streams . Another proposal is to use electricity of nuclear power plants to heat the CO2 / alkanolamine liquid .Nuclear power plants need a constant running, no peaks, no downs. That would be ideal for a CCS unit, which is also running more or less constant.The renewable energies are much less constant, as dependent from the weather.That the nuclear power plants are seen as something we have to get rid of as soon as possible, is wrong, I think. The problem is reworking and storage of the final residues, and these can be solved, but politicians were / are blind for this issue so far.When CO2 can be stored in deep wells under a saline barrier, why is this not possible with waste from nuclear power plants?It is clear to me that without CCS projects the world cannot achieve the CO2 emission targets .

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Peter Stilbs (December 14, 2015 11:10 PM)

CCS is a totally absurd idea - even to match present day emissions requires "plants" magnitudes larger than any chemical industry today, and enormous quantities of energy. Instead, let plants, algae and trees handle all this for free. They NEED this CO2 - and animal life on Earth totally depends on them too.

in today's politically correct World any mention of positive effects of CO2 emissions to the atmosphere is normally automatically met by hostile reactions of various kinds -

Regardless of that aspect and whether CO2 actually is a major climate driver it should be rather obvious to any thinking and educated person that carbon sequestration underground or capture by chemical means is a totally futile and mis-guided idea in any case. Just matching present-day emissions would require chemical plats 1000 times larger than any existing chemical or other industry, using up all available energy and other resources, and surely cause a grade of pollution unseen before.

The matter was discussed some years ago e.g. here https://www.newscientist.com/article/mg21428593-800-stripping-co2-from-air-requires-largest-industry-ever/

Norwegians abandoned their Mongstad sequestration project some years ago after pouring several billions into it - although it doubled as a means of pressing more oil out of the wells, where storage was meant to be made

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David Gedymin (December 14, 2015 11:15 PM)

Saying it is totally absurd is rather hyperbolic. 'Magnitudes' meaning what scale? Adding an Acid Gas Recovery unit and CO2 compressors might increase the plot space by 20-40%, but that certainly isn't 'magnitudes'.

There may be some local benefits to increased emissions. The hostility from people might come from somebody pointing out some benefits as though it outweighs the much more concerning impacts on climate change. Remember, this is about mitigating rapid human-caused climate that seems to be upsetting global weather patterns and ecosystems. This isn't about saving the planet itself - the planet will be fine. It's about keeping it habitable in the near-future so that humanity can adapt to climate that changes at a normal pace.

Again, where are you coming up with the idea that this would require plants 1000x times larger? That newscientist.com article you've cited is talking about scrubbing CO2 from dry atmospheric air, where the concentration of CO2 is only around 400 ppm. This is a drastically different scenario from scrubbing flue gas or syngas, where the concentration is closer to 23 mol%. Of course trying to efficiently remove CO2 at a concentration of 0.04% is absurd.

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Joe Ellebracht (January 29, 2017 12:11 PM)

CCS that results in a pure stream of CO2 to be sequestered deep underground is a bandaid approach. Ideally the CO2 would be turned into something useful, or failing that, into something solid that can be exposed to the atmosphere. Vast greenhouses with enhanced CO2 atmospheres next to power plants might be an option, with the greenhouses containing rapidly growing woody bushes or dwarf trees. Over time, these could be harvested and turned into pulp or lumber or an engineered wood product like plywood or chipboard. This would require plenty of land. Once the plantlife was established, the greenhouse structure itself would be superfluous, and could be moved to another location nearby, fairly easily if constructed as a temporary tent.